Orthodontics is a specialty of dentistry that is concerned with the study and treatment of malocclusions which can result from tooth irregularities, disproportionate facial skeleton relationships, or both. Orthodontics treats malocclusion through the displacement of teeth via bony remodeling and control and modification of facial growth.
This process has been traditionally accomplished by using static mechanical force to induce bone remodeling, thereby enabling teeth to move. In this approach, braces having an archwire interface with brackets are affixed to each tooth. As the teeth respond to the pressure applied via the archwire by shifting their positions, the wires are again tightened to apply additional pressure. This widely accepted approach to treating malocclusions takes about twenty-four months on average to complete, and is used to treat a number of different classifications of clinical malocclusion. Treatment with braces is complicated by the fact that it is uncomfortable and/or painful for patients, and the orthodontic appliances are perceived as unaesthetic, all of which creates considerable resistance to use. Further, the treatment time cannot be shortened by increasing the force, because too high a force results in root resorption, as well as being more painful. The average treatment time of twenty-four months is very long, and further reduces usage. In fact, some estimates provide that less than half of the patients who could benefit from such treatment elect to pursue orthodontics.
Kesling introduced the tooth positioning appliance in 1945 as a method of refining the final stage of orthodontic finishing after removal of the braces (debanding). The positioner was a one-piece pliable rubber appliance fabricated on the idealized wax set-ups for patients whose basic treatment was complete. Kesling also predicted that certain major tooth movements could also be accomplished with a series of positioners fabricated from sequential tooth movements on the set-up as the treatment progressed. However, this idea did not become practical until the advent of three-dimensional (3D) scanning and use of computers by companies including Align Technologies and as well as OrthoClear, ClearAligner, and ClearCorrect to provide greatly improved aesthetics since the devices are transparent.
However for traditional trim model to individual tooth, the gum geometry is lost and the fake gum is recreated, often remodeled by a technician. Hence, the gum geometry may not be accurate at first and an animation of gum changes over time due to lack of a physical model is even harder to model. Such inaccurate modeling causes the resulting aligner to be mismatched resulting in devices which are too large or too small resulting in patient discomfort.
Another problem is that without the real gum as the reference, some so-called modeled treatments cannot be achieved in reality resulting in potential errors, e.g., a tooth movement can occur within a mis-modeled gingival, however, the tooth movement may actually be moved exteriorly of a patient's real gingival.
Another problem of trimming and hole filling and creating an individual tooth and gum model is there is little information that can define the real boundary of two teeth. Such trim and fill models force the boundary surfaces to be defined even if they are arbitrary.
Depending on what boundary surface is defined, the movement can be restricted or relax, meaning some real life movement can be achieved; however, due to such inaccuracies, the modeling software is unable to model accurately due to models colliding into each other. This may cause the real treatment outcome to create gaps between teeth and further requiring final refinements which increase cost and patient dissatisfaction. On the other hand, if the modeled movement is relax, the software may enable movements which are physically impossible in reality and this may cause the modeled device to push teeth into one another unable to move. This may also cause the plastic shell of the aligner to sometimes stretch so much that the shell applies an uncomfortable amount of force, which could be painful, to a patient.
Another problem of trim and hole fill is the filling of the geometry like a real tooth, for below, the below lines are likely of boundary surfaces modeled, such models look like a real tooth; however, such sharp boundaries cause deeper undercuts which, once printed and thermal formed to have a plastic shell, make removal of the plastic shell from the printed model difficult due to the deep undercuts. To compensate for this, a bevel object is typically created to fill the clevis increasing inaccuracy and costs.
Another problem of trim and hole filling is the model size is too large to communicate between the user and manufacturer thus requiring that the model size be reduced resulting in missing model details. These inaccuracies could misguide professionals, e.g., the full complex model may not show a gap between two adjacent teeth however the reduced model may show one.
These 3D scanning and computerized planning treatments are cumbersome and time consuming. Accordingly, there exists a need for an efficient and cost effective procedure for planning the orthodontic treatment of a patient.